Be more lazy and slack off

uniseg/graphemes/stream.scm

@@ -15,14 +15,19 @@
 
 ;; TODO: the golang uniseg also does word and sentence boundaries. These state machines could be implemented if we wanted to.
 (define-immutable-record-type <grapheme>
-  (make-grapheme glyphs width)
+  (make-grapheme width glyphs-promise string-promise)
   grapheme?
-  (glyphs grapheme-glyphs)
-  (width grapheme-width))
+  (width grapheme-width)
+  (glyphs-promise _grapheme-glyphs-promise)
+  (string-promise _grapheme-string-promise))
+
+(define (grapheme-glyphs grapheme)
+  "Return a lazily-constructed list of glyphs in the grapheme"
+  (force (_grapheme-glyphs-promise grapheme)))
 
 (define (grapheme-string grapheme)
-  "Given a grapheme, construct a string representing it."
-  (list->string (grapheme-glyphs grapheme)))
+  "Return a lazily-constructed string of the glyphs in the grapheme."
+  (force (_grapheme-string-promise grapheme)))
 
 (define (string->grapheme-stream str)
   "Given a string, create a (lazy) stream of graphemes."
@@ -117,8 +122,8 @@
       (else (values 'any #t))))
 
 
-  (define grapheme-width 0)
   (define glyphs-reverse '())
+  (define grapheme-width 0)
 
   (define hit-eof #f)
 
@@ -147,6 +152,8 @@
    stream-null
    (stream-cons
     (make-grapheme
-     (reverse glyphs-reverse)
-     grapheme-width)
+     grapheme-width
+     ;; Delay to avoid construction of unnecessary lists and strings!
+     (delay (reverse-list->string glyphs-reverse))
+     (delay (reverse glyphs-reverse)))
     (input->grapheme-stream port))))